This invention relates generally to medical electrical leads, and more particularly to implantable medical electrical leads of the type employing in-line, bipolar connectors having rotatable connector pins for transmitting torque along the body of the lead.
An early medical electrical lead with a rotatable connector pin is disclosed in U.S. Pat. No. 4,106,152, issued to Bisping. In the Bisping lead, a unipolar connector was used, the connector being comprised of a conductive connector pin and an insulative sleeve. Both the connector pin and the insulative sleeve were free to rotate relative to the body of the lead. In more modern designs, such as employed in commercially marketed pacing leads, only the connector pin rotated, and the insulative portion of the connector, typically used to seal the lead within the connector housing of an implantable electrical pulse generator, is fixed relative to the body of the lead. Examples of such connector assemblies are shown in U.S. Pat. No. 4,628,943 issued to Miller, U.S. Pat. No. 4,467,687 issued to Peers-Travarton, U.S. Pat. No. 4,577,643 issued to Baraneck, U.S. Pat. No. 4,402,329 issued to Williams, and U.S. Pat. No. 4,463,765 issued to Gold.
While most early screw in leads were unipolar leads, there has been a considerable interest in the development of practical bipolar screw-in leads in the past few years. One such design is disclosed in the Miller patent, discussed above. Other bipolar screw-in leads having in-line connectors include the Medtronic Model 4016 pacing lead and the Osypka PY-66 bipolar screw-in pacing lead. In all three leads, the connector assembly comprises a rotatable connector pin having an exposed length which is intended to be coupled to a first connector attached to a pacemaker, and a connector ring intended to be coupled to a second connector attached to the pacemaker. The exposed portion of the connector ring is separated from the exposed portion of the connector pin by an insulative sleeve, in all three leads.
In the Miller patent, discussed above, the connector pin extends only a short distance into the connector assembly, and is rotatably mounted within the connector assembly by means of a circumferential groove in the pin, located within a corresponding inwardly facing circular ridge in the connector assembly. In the Model 4016, the connector pin is rotatably mounted by means of an expanded diameter section of the connector pin, located coaxially within the insulative member separating the connector pin and connector ring. The expanded diameter portion of the connector pin is retained within the connector assembly by means of a first shoulder, proximal to the ring electrode, within the insulative member and by a second shoulder, proximal to the first shoulder. The insulative member included corresponding inward facing circumferential shoulders, engaging the first and second shoulders of the connector pin. An exploded drawing of the connector of the Model 4016 pacing lead can be found in the article "The Impact of Pending Technologies on a Universal Connector Standard", by Doring, et al, PACE, Vol. 9, pp. 1186-1190, 1986.
In the Osypka lead, the rotating connector pin is also retained within the connector assembly by means of an expanded diameter section of the connector pin, located within the connector assembly. In the Osypka lead, the expanded diameter section is located proximal to the connector ring, at the distal end of the connector pin. The expanded diameter section includes a first circumferential shoulder facing the proximal end of the connector pin, which engages the corresponding distally facing circumferential shoulder in the insulative portion of the connector assembly. It appears that distal movement of the connector pin is prevented only by means of the distal end of the connector pin abutting the proximal end of an insulative sleeve covering the coiled conductor to which the connector pin is attached. The Osypka electrode is notable in that it also includes a metal bearing sleeve located circumferential to the connector pin, proximal to the expanded diameter portion of the pin.